1. Field of the Invention
This invention relates generally to the field of packaging, and more specifically to molded plastic containers of the type that have neck or finish portion that is constructed and arranged to form a seal with respect to a closure.
2. Description of the Related Technology
Plastic containers are typically fabricated using either injection molding or one of two types of blow molding. The blow molding process is characterized by using internal pressure to force a hot, soft plastic preform or parison against a molding surface. Blow molding can be performed using either a reheat stretch blow molding process, which is typical for plastic containers that are fabricated from polyethylene terephthalate (PET), or an extrusion blow molding process, which is typical for containers that are fabricated from such materials as high-density polyethylene and polyolefins.
In the extrusion blow molding process, a molten tube or parison is continuously extruded from an extrusion fixture. A mold assembly that moves at a speed that is substantially equal to the speed of the extruded parison periodically captures portions of the parison, and pressurization as applied to inflate the captured portion of the parison against the interior surfaces of the mold assembly. The mold assembly is typically mounted for motion on either a molding wheel, which moves in a circular path, or on a shuttle, which moves the mold assembly on a substantially straight path.
Plastic containers typically include a neck or finish portion having an opening that is in communication with the interior space of the container. In some instances, the neck or finish portion is threaded to permit application of a closure. In other cases, structure is molded into the neck or finish portion to permit a closure to be snapped on. The neck or finish portion typically includes at least one sealing surface that is adapted to bear against a portion of a closure in order to form a liquid tight seal with respect to the closure when it is properly applied.
As is shown in FIGS. 1 and 2, one type of conventional plastic container 10 includes a main body portion 12 and a neck portion 14. The neck portion 14 has an upper lip 16 that defines an opening and a sealing surface 18 that is constructed and arranged to form a seal with respect to an applied closure. A molded feature such as an anti-rotation lug 20 is provided adjacent to the neck portion. The anti-rotation lug 20 had a generally triangular shape when viewed in side elevation, with a first inclined side surface 24, a second inclined side surface 26 and a solid outer surface 22 facing away from the neck portion 14. It had a maximum width W1, a maximum height H1 and a maximum radial depth D1. The anti-rotation lug 20 functioned to prevent or deter a closure from being unscrewed from the neck portion 14 by a consumer after it has been applied by the manufacturer. In the case of such containers, the anti-rotation lug 20 was integral with the neck portion 14 at a part of the neck portion 14 that was nearby the sealing surface 18.
Some of these containers 10 experienced a deformation condition known as ovalization, in which the neck or finish portion 14 deviated from its ideal substantially cylindrical shape. This created sealing problems with respect to an applied closure. The inventors herein have identified a cause of such ovalization as being uneven shrinkage of the neck or finish portion after the hot molded container is removed from the mold. It has been determined that the thermal mass of the anti-rotation lug was a significant factor in causing the uneven shrinkage.
A need exists for an improved molded plastic container having a neck or finish portion that is adjacent to a molded feature that is less susceptible to deformation as a result of uneven cooling after the container has been removed from the mold. A need also exists for a method of correcting a sealing problem in such a container that is caused at least in part by the presence of the molded feature.